Abstract
Myosin heavy chain (MyHC) isoforms consist of Myh7, Myh2, Myh1, and Myh4, which are expressed in skeletal muscle tissues during postnatal development. These genes influence the contraction–relaxation activity in skeletal muscles and are involved in determining muscle composition such as the proportion of fast-to-slow and/or slow-to-fast fiber types. Among them, Myh1 is associated with skeletal muscle contraction and is involved in both slow-to-fast and fast-to-slow transition. However, the muscle transition mechanism is not well understood. For this study, we first produced porcine Myh1 transgenic (TG) mice to study whether the ectopic expressed porcine Myh1 gene had any effects on muscle composition, especially on slow-type muscle components. Our results showed that the factors associated with slow muscles, such as Myh7, Myoglobin, Troponin (slow-type units), and cytochrome C, were highly expressed in the quadriceps muscles of Myh1 transgenic mice. Furthermore, the ectopic porcine MYH1 protein was located only in the slow-type muscle fibers of the quadriceps muscles in Myh1 transgenic mice. In physical endurance tests, Myh1 transgenic mice ran longer and further on a treadmill than wild-type (WT) mice. These data fully supported our hypothesis that Myh1 is associated with slow muscle composition, with overexpression of Myh1 in muscle tissues possibly being a new key in modulating muscle fiber types. Our study provides a better understanding of muscle composition metabolism, physical mobility, and genetic factors in muscle fatigue.
Highlights
Skeletal muscle is composed of slow (Type I) and fast (Type II) fibers, which convert chemical energy into energy for contraction and metabolism [1,2,3]
We verified gene expression patterns of the myosin heavy chain (MyHC) family in various porcine tissues using reverse transcription polymerase chain reaction (RT-PCR), and the data showed that Myh7 and Myh2 are expressed in the brain, lung, muscle, and testis
The overexpression of Myh1 affected the up-regulation of factors that are associated with slow muscle fibers, and exercise endurance was increased in the ectopic overexpressed Myh1 TG mouse, which represents muscle oxidative capacity
Summary
Skeletal muscle is composed of slow (Type I) and fast (Type II) fibers, which convert chemical energy into energy for contraction and metabolism [1,2,3]. Adult skeletal muscles have four myosin heavy chain (MyHC) isoforms, which are namely Myh (Type I), Myh (Type IIA), Myh (Type IIX), and Myh (Type IIB) These show distinct expression patterns in troponin, myosin light chain, and sarcoplasmic calcium dependent ATPase [6,7,8]. Different expression patterns in MyHC isoforms, which appear in fast-to-slow or slow-to-fast fiber transition, are caused by neuromuscular activity, hormones, and mechanical loading and unloading [12]. Another specific fiber isoform consists of three types of troponin subunits, which are namely tropomyosin, myosin light chain, and various calcium regulatory proteins [13]. Our study showed that pig Myh is associated with the activation of the slow muscle components by increasing the expression level of slow muscular sarcomere-associated genes, which increases the overall physical endurance capacity
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